1. Field of the Invention
This invention relates to the field of thin windows for high pressure enclosures and, more particularly, this invention relates to windows for high pressure enclosures that are transparent to x-ray radiation.
2. Background of the Invention
Detailed spray analysis is important to the overall aim of increasing combustion efficiency and reducing emissions of pollutants. An understanding of the liquid breakup mechanism close to the nozzle has significant bearing on the design of nozzle geometry and is key to realistic computer modeling. The subject of the experiments can be fast, transient phenomena including but not limited to supercritical fluid, high-pressure liquid, and gas injection, and plasma-material interactions, such as the fuel spray injected into a pressurized chamber that mimics realistic internal combustion engine cylinder operating conditions. These analysis must be run in a high pressure environment so as to mimic that of fuel injection systems.
Such high pressure enclosures contain windows for optical scrutiny of fluid flows occurring within the enclosures. Such windows have been in increasing demand, not only for fuel injection scenarios, but also for real-time studies of a variety of chemical reactions and other phenomena.
The materials involved in some phenomena under observation are often opaque to visible light due to highly dense droplets surrounding the core region of the events. Although significant advances in laser diagnostics have been made over the last 20 years, the region close to the nozzle has remained impenetrable due to opacity of the fuel.
With the advent of high intensity x-ray and other radiation sources, emerging radiation-imaging techniques are increasingly used to acquire ultra-fast two-dimensional (2D) radiation images of extended size and with high spatial resolution.
On the other hand, X-ray images yield quantitative information and yet are non-intrusive. By utilizing monochromatic x-radiography one can probe the characteristics of a myriad of events. In order to make these experiments possible in a variety of settings there is a need in the art for critical sample environmental chambers that are accessible to x-rays and other radiation for quantitative and time-resolved analysis.
However, view finders for use with these high pressure environments which provide near transparent scrutiny of x-ray interaction remain elusive. The attenuation of x-rays in a material is a steeply increasing function of the atomic number of the material, so that only low atomic number materials are suitable constituents for x-ray transparent windows. Beryllium is the commonly used material for x-ray-transparent windows. However, the health-hazardous nature of this brittle metal prohibits it from being a proper material for a window for a pneumatically pressurized enclosure because any breakage results in the wide dispersal of toxic materials. Beryllium is likely to break because its stiffness tends to cause fractures if the material is under tension. The same is true for other light-element (low atomic number) materials, such as diamond. Yet the development of practical radiation-transparent windows for high-pressure chambers has been an intensive area of research emphasizing the search for new types of materials that meet the rigorous requirements imposed by high-pressure conditions.
Thin x-ray transparent polymer windows have been used for enclosures where the pressure difference across the window did not exceed approximately one atmosphere. Such windows are disclosed in U.S. Pat. Nos. 4,933,557 (1990, to Perkins et al), 5,585,644 (1996, to Van der Borst) and 6,233,306 (2001, Van Sprang).
A need exists in the art for light-element windows with tensile strength higher than 200 MPa (one atmosphere=0.1 Ma) that can withstand high pressures (Many Aluminum alloys have tensile strength in the 124-200 MPa range. Moreover, Aluminum has too high X-ray absorption). The windows should be radiation-transparent. Furthermore, the windows should not comprise hazardous materials in the event breakage occurs.